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Biomedical subjects

K Yoon

Publications and source records attributed to K Yoon.

At least 37 records · Page 2Linked to original sources
PubMed2000

An area for vergence eye movement in primate frontal cortex.

To view objects at different distances, humans rely on vergence eye movements to appropriately converge or diverge the eyes and on ocular accommodation to focus the object. Despite the importance of these coordinated eye movements (the 'near response') very little is known about the role of the cerebral cortex in their control. As near-response neurons exist within the nucleus reticularis tegmenti pontis, which receives input from the frontal eye field region of frontal cortex, and this cortical region is known to be involved in saccadic and smooth-pursuit eye movements, we propose that a nearby region might play a role in vergence and ocular accommodation. Here we provide evidence from rhesus monkeys that a region of frontal cortex located immediately anterior to the saccade-related frontal eye field region is involved in vergence and ocular accommodation, and in the sensorimotor transformations required for these eye movements. We conclude that the macaque frontal cortex is involved in the control of all voluntary eye movements, and suggest that the definition of the frontal eye fields should be expanded to include this region.

Accommodation, Ocular↗
PubMed2000

The 2.0 A crystal structure of cephalosporin acylase.

BACKGROUND: Semisynthetic cephalosporins are primarily synthesized from 7-aminocephalosporanic acid (7-ACA), which is usually obtained by chemical deacylation of cephalosporin C (CPC). The chemical production of 7-ACA includes, however, several expensive steps and requires thorough treatment of chemical wastes. Therefore, an enzymatic conversion of CPC to 7-ACA by cephalosporin acylase is of great interest. The biggest obstacle preventing this in industrial production is that cephalosporin acylase uses glutaryl-7ACA as a primary substrate and has low substrate specificity for CPC. RESULTS: We have solved the first crystal structure of a cephalosporin acylase from Pseudomonas diminuta at 2.0 A resolution. The overall structure looks like a bowl with two "knobs" consisting of helix- and strand-rich regions, respectively. The active site is mostly formed by the distinctive structural motif of the N-terminal (Ntn) hydrolase superfamily. Superposition of the 61 residue active-site pocket onto that of penicillin G acylase shows an rmsd in Calpha positions of 1.38 A. This indicates structural similarity in the active site between these two enzymes, but their overall structures are elsewhere quite different. CONCLUSION: The substrate binding pocket of the P. diminuta cephalosporin acylase provides detailed insight into the ten key residues responsible for the specificity of the cephalosporin C side chain in four classes of cephalosporin acylases, and it thereby forms a basis for the design of an enzyme with an improved conversion rate of CPC to 7-ACA. The structure also provides structural evidence that four of the five different classes of cephalosporin acylases can be grouped into one family of the Ntn hydrolase superfamily.

Amino Acid Sequence↗
PubMed2000

Ligand structure-dependent differences in activation of estrogen receptor alpha in human HepG2 liver and U2 osteogenic cancer cell lines.

Differences in ligand-activation of estrogen receptor alpha (ER(alpha)) were investigated in human HepG2 liver carcinoma and U2 osteogenic sarcoma cells transfected with wild-type ER (ER-wt) and variants expressing only activation function 1 (ERAF1) or AF2 (ER-AF2). The estrogen-responsive C3-luc construct containing the complement C3 gene promoter linked to a bacterial luciferase reporter gene was used to determine ligand-induced wild-type or variant ER activation. The quality pattern of ER-dependent responses was similar in both cell lines for a series of weakly estrogenic hydroxy and dihydroxyaromatic compounds including p-octylphenol, p-nonylphenol, 2',4',6'-trichloro-4-biphenylol, 2',3',4', 5'-tetrachloro-4-biphenylol, bisphenol A and 2, 2'-bis(p-hydroxyphenyl)-1,1,1-trichloroethane. However, some significant quantitative differences in these compounds were also observed. The weakly estrogenic pesticide, kepone, and the phytoestrogens, resveratrol (a trihydroxystilbene) and naringen (a flavanone), induced distinctly different patterns of responses; induction by these compounds was not observed in either cell line cotransfected with ER-wt or ER-AF2. In contrast, naringen activated ER-AF1 in HepG2 cells and resveratrol activated ER-AF1 in U2 cells. In HepG2 cells cotreated with E2 plus the estrogenic compounds, only BPA and resveratrol exhibited ER(alpha) antagonist activity. Structure-dependent differences in ER(alpha) activation and inhibition are consistent with the increasingly complex patterns of ER action in various tissues and indicate that the estrogenic activity of an individual compound can only be determined by using an extensive testing protocol.

Animals↗
PubMed2000

Gene correction by RNA-DNA oligonucleotides.

An oligonucleotide composed of a contiguous stretch of RNA and DNA residues has been developed to facilitate the correction of single-base mutations of episomal and chromosomal targets in mammalian cells. The design of the oligonucleotide exploited the highly recombinogenic RNA-DNA hybrids and featured hairpin capped ends avoiding destruction by cellular helicases or exonucleases. The RNA-DNA oligonucleotide (RDO) was designed to correct a point mutation in the tyrosinase gene and caused a permanent gene correction in mouse albino melanocytes, determined by clonal analysis at the level of genomic sequence, protein and phenotypic change. Recently, we demonstrated correction of the tyrosinase gene using the same RDO in vivo, as detected by dark pigmentation of several hairs and DOPA staining of hair follicles in the treated skin of albino mice. Such RDOs might hold a promise as a therapeutic method for the treatment of skin diseases. However, the frequency of gene correction varies among different cells, indicating that cellular activities, such as recombination and repair, may be important for gene conversion by RDOs. As this technology becomes more widely utilized in the scientific community, it will be important to understand the mechanism and to optimize the design of RDOs to improve their efficiency and general applicability.

Albinism↗
PubMed2000

Localized in vivo genotypic and phenotypic correction of the albino mutation in skin by RNA-DNA oligonucleotide.

We recently demonstrated that an RNA-DNA oligonucleotide corrected a point mutation in the mouse tyrosinase gene, resulting in permanent and inheritable restoration of tyrosinase enzymatic activity, melanin synthesis, and pigmentation changes in cultured melanocytes. In this study, we extended gene correction of melanocytes from tissue culture to live animals, using a chimeric oligonucleotide designed to correct a point mutation in the tyrosinase gene. Both topical application and intradermal injection of this oligonucleotide to albino BALB/c mouse skin resulted in dark pigmentation of several hairs in a localized area. The restored tyrosinase enzymatic activity was detected by dihydroxyphenylacetic acid (DOPA) staining of hair follicles in the treated skin. Tyrosinase gene correction was also confirmed by restriction fragment length polymorphism analysis and DNA sequencing from skin that was positive for DOPA staining and melanin synthesis. Localized gene correction was maintained three months after the last application of the chimeric oligonucleotides. These results demonstrated correction of the tyrosinase gene point mutation by chimeric oligonucleotides in vivo.

Administration, Cutaneous↗
PubMed2000

Synthesis and pharmacological evaluations of N-(substituted benzoylamino)-5-carbethoxymethyl-1,2,3,6-tetrahydropyridines as potential antiinflammatory agents.

In a continuing effort to enhance antiinflammatory activities, a series of 1,2,3,6-tetrahydropyridines, 4-tert butyl (9a), 4-methoxy (9b), 2-fluoro (9c), 3-chloro (9d) and 3,4-dichloro (9e) benzoylamino-5-carbethoxymethyl-1,2,3,6-tetrahydropyridines, were synthesized and evaluated for their antiinflammatory activities. Antiinflammatory activities were screened in animal models employing carrageenan induced paw-edema assay on the male Sprague-Dawley rat. Relative potencies for carrageenan induced paw-edema assay were 1, 0.07, > 0.03, 0.14, 0.4 and 0.12 for indomethacin (IC50 = 3 mg/kg), 9a, 9b, 9c, 9d and 9e, respectively. These novel tetrahydropyridines were assessed for nonsteroidal antiinflammatory drug-mediated inhibition of nitric oxide generation in RAW 264.7 macrophage cell line using Griess' reagent. Relative potencies for inhibition of nitric oxide generation by macrophages stimulated with lipopolysaccharide (1 microgram/ml) were 1, 0.48, 0.44, 0.43, 0.45 and 0.45 for indomethacin (IC50 = 0.434 mM), 9a, 9b, 9c, 9d and 9e, respectively. The results show that novel tetrahydropyridines have moderate antiinflammatory activities and that they inhibit nitric oxide production by inhibiting inducible nitric oxide synthase.

Animals↗
PubMed1999

A sequence-specific gene correction by an RNA-DNA oligonucleotide in mammalian cells characterized by transfection and nuclear extract using a lacZ shuttle system.

The variability in gene conversion frequency by an RNA-DNA oligonucleotide (RDO) prompted us to develop a system as a means of measuring the conversion frequency rapidly and reproducibly. A shuttle vector was constructed to measure the frequency of targeted gene correction by RDO of the E. coli beta-galactosidase gene containing a single point mutation (G --> A), that resulted in inactivation of enzymatic activity. An RDO corrected the point mutation and restored the enzymatic activity, approximately 1%, determined by a histochemical staining in mammalian cells and by a color selection (blue or white) of bacteria transformed with Hirt DNA. In addition, we established an in vitro system capable of gene correction using nuclear extracts. CHO-K1 nuclear extracts corrected the point mutation approximately 0.1%, determined by bacterial transformation. Using the in vitro reaction, frequency of gene conversion in different cell types was measured. The embryonic fibroblasts from p53-/- mouse showed higher gene correction than that of the isogenic p53+/+ cells. Nuclear extracts from DT40 cells, which have a higher homologous recombination rate than any other mammalian cells exhibited 0.1-0.6% of gene correction. These results indicated that recombination may be rate-limiting in gene conversion by RDO in cells with competent mismatch repair activities. Utilizing transfection and in vitro reaction, we demonstrated that such a shuttle system might be useful in comparing the frequency of targeting among different cell types and to investigate the mechanism of gene conversion by RDO.

Animals↗
PubMed1998

The value of screening for psychiatric disorders in rheumatology referrals.

BACKGROUND: Musculoskeletal complaints are common and often unexplained and often lead to rheumatology referrals. The prevalence of psychiatric disease in patients with musculoskeletal complaints is unknown. OBJECTIVES: To determine the prevalence of common psychiatric disorders among patients referred to a rheumatology clinic and the likelihood of establishing a rheumatic diagnosis if a psychiatric disorder is present. DESIGN: Prospective diagnostic survey. SETTING: Two hospital-based rheumatology clinics and a general medicine clinic. PARTICIPANTS: A consecutive sample of newly referred patients (n = 185) and their rheumatologists (n = 9). INTERVENTION: Before their visit, all patients filled out a self-administered version of PRIME-MD (Primary Care Evaluation of Mental Disorders), a questionnaire that makes Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition: Primary Care Version, diagnoses of depressive, anxiety, and somatoform disorders. After the visit, the study rheumatologists, who were unaware of the PRIME-MD results, completed a questionnaire regarding their diagnostic assessment. These patients were compared with 210 patients with musculoskeletal complaints who were cared for in a general medicine clinic. MAIN OUTCOME MEASURES: Psychiatric and rheumatic disorders. RESULTS: Compared with patients with musculoskeletal complaints in a general medicine clinic, patients referred to a rheumatology clinic had a higher prevalence of psychiatric disease (40% vs 29%; P = .008), had an almost 2-fold higher prevalence of anxiety disorders, and were more likely to have multiple psychiatric disorders (odds ratio = 2.70, 95% confidence interval = 1.50-5.00). The likelihood of a psychiatric disorder differed among patients with connective tissue disease, nonsystemic articular or periarticular disorders, and nonarticular disorders (27%, 38%, 55%, respectively; P = .006). In a best-fitting logistic regression model, psychiatric disorders markedly decreased the likelihood of a connective tissue disease (odds ratio = 0.24, 95% confidence interval = 0.09-0.62). CONCLUSIONS: Forty percent of patients referred to a rheumatology clinic in this study had a psychiatric disorder, and its presence predicted a lower likelihood of a connective tissue disease. Prospective studies are needed to determine if screening for psychiatric disease before referring patients with unexplained musculoskeletal complaints would reduce costs or improve recognition of potentially treatable psychiatric disorders.

Adolescent↗
PubMed1998

Phylogenetic analysis of the nef gene reveals a distinctive monophyletic clade in Korean HIV-1 cases.

To study the genetic variation of the HIV-1 strains prevalent in South Korea, we analyzed the nef sequences derived from 46 HIV-1-positive individuals living in various geographic regions in Korea. Phylogenetic analysis revealed four subtypes of HIV-1: A (3 patients), B (41 patients), D (1 patient), and a type that could not be clearly classified to any known subtype (1 patient). Thirty-five of the 41 Korean subtype B isolates formed a distinct monophyletic clade that is not related to any of the international sequences from the Los Alamos Database or GenBank as of June 1997. Indeed, the presence of unique conserved sequences was identified among the Korean isolates in this Korean subtype B group. The variations in the nucleotide sequences of a majority (32 of 35) subtype B samples within the Korean clade were 1.9% to 8.8%, and amino acid sequences varied from 3.9% to 15.5%. These results suggest that HIV-1 strains currently present in South Korea might have originated from a few sources or might be developing through a certain selective pressure. This is the first report on the molecular nature of the HIV-1 infection present in South Korea.

Adolescent↗
PubMed1998

Growth properties of HSIVnef: HIV-1 containing the nef gene from pathogenic molecular clone SIVmac239.

To elucidate the function of nef, we constructed infectious chimeric clones between human immunodeficiency virus type 1 (HIV-1) and simian immunodeficiency virus (SIV) of macaques, by deleting a part of the nef sequence from the HIV-1 genome and inserting the entire nef gene from the pathogenic molecular clone, SIVmac239. We have named this construct HSIVnef. While there was no difference in the replication kinetics of HSIVnef+ and HSIVnef- in transformed cell lines, there was a profound difference in the replication of these virus in primary cells. These data indicated that the SIV nef gene could complement the functions of the HIV-1 nef gene in the context of the HIV-1 genome, providing further evidence that results observed in the macaque model are relevant to HIV infections in man. HSIVnef is a useful model for the study of the nef gene.

Animals↗
PubMed1998

Stable and inheritable changes in genotype and phenotype of albino melanocytes induced by an RNA-DNA oligonucleotide.

Experimental strategies have been developed to correct point mutations using chimeric oligonucleotides composed of RNA and DNA. We used these RNA-DNA oligonucleotides to correct a point mutation in mouse tyrosinase, a key enzyme for melanin synthesis and pigmentation. Melanocytes derived from albino mice contain a homozygous point mutation (TGT-->TCT) in the tyrosinase gene, resulting in an amino acid change from Cys-->Ser. Correction of this point mutation results in the restoration of tyrosinase activity and melanin synthesis, thus changing the pigmentation of the cells. Upon transfection of the RNA-DNA oligonucleotide to albino melanocytes, we detected black-pigmented cells and isolated multiple single clones. All black-pigmented clones exhibited a correction of the point mutation in a single allele of the tyrosinase gene. A full-length tyrosinase was detected by an antityrosinase antibody, and the enzymatic activity was restored in all converted black-pigmented clones. Only degraded fragments were detected in albino cells due to proteolytic cleavage of mutant tyrosinase. The phenotype and genotype of converted black-pigmented clones was stable. These results demonstrate a permanent and stable gene correction by the RNA-DNA oligonucleotide at the level of genomic sequence, protein, and phenotypic change by clonal analysis.

Amino Acid Sequence↗
PubMed1998

p53 mutations and human papillomavirus DNA in oral squamous cell carcinoma: correlation with apoptosis.

Forty-two oral squamous cell carcinomas (SCCs) were analysed for p53 mutations and human papillomavirus (HPV) infection to examine the prevalency of these factors and correlation with apoptotic index (AI; number of apoptotic cells per 100 tumour cells) of the tumour tissue. In polymerase chain reaction (PCR)-Southern blot analysis, HPV DNAs were detected from 22 out of 42 SCCs (52%) with predominance of HPV-16 (68%). p53 mutations in exons 5-8, screened by nested PCR-single-strand conformation polymorphism (PCR-SSCP) analysis, were observed in 16 of 42 tumours (38%). The state of the p53 gene did not show any correlation with HPV infection. The terminal deoxynucleotidyl transferase (TdT)-mediated dUTP-biotin nick end labelling (TUNEL) method was used for detection of apoptotic cells. The mean AI was 2.35, ranging from 0.31 to 6.63. SCCs associated with p53 mutation had significantly lower AI than those without p53 mutation (P < 0.01), whereas no difference in AI was found between SCCs with and without HPV infection. The results of this study confirmed that HPV infection and/or p53 mutations are implicated, but are not mutually exclusive events, in carcinogenesis of oral SCC and also showed that decrease in apoptosis is more closely related to p53 mutation than HPV infection.

Apoptosis↗
PubMed1998

Different frequency of gene targeting events by the RNA-DNA oligonucleotide among epithelial cells.

A unique hybrid oligonucleotide composed of both RNA and DNA has been shown to correct a point mutation in a site-specific and inheritable manner in extrachromosomal and chromosomal targets. In order to develop new gene therapeutics for skin, we tested two oligonucleotides that were shown to create a point mutation in alkaline phosphatase and beta-globin genes in several epithelial cell types. Highly transformed epithelial cells (HeLa) exhibited a conversion frequency of 5% by both RNA-DNA oligonucleotides. In comparison, other immortalized epithelial cells (HaCaT) or human primary keratinocytes did not show any detectable level of gene conversion by the restriction fragment length polymorphism analysis, indicating less than 1% conversion frequency. The concentration of the oligonucleotide in the nuclei of HeLa cells was similar to that of HaCaT or human primary keratinocytes measured by a radiolabeled or a fluorescein-conjugated oligonucleotide. Moreover, the RNA-DNA oligonucleotide exhibited a prolonged stability in the nucleus. Thus, neither uptake nor nuclear stability of the oligonucleotide appears to be a limiting factor in gene targeting events under our experimental conditions. These results indicate that the frequency of gene targeting varies among different cells, suggesting that cellular recombination and DNA repair activities may be important.

Alkaline Phosphatase↗
PubMed1998

IGF-I binding proteins, IGF-I binding protein mRNA and IGF-I receptor mRNA in rats with acute renal failure given IGF-I.

BACKGROUND: Recombinant human insulin-like growth factor-I (rhIGF-I) accelerates recovery from acute renal failure (ARF) in rats. IGF-I acts through the IGF-I receptor (IGF-IR) and its actions may be modified by IGF-I binding proteins (IGFBPs). It therefore would be of value to determine the effects of both ARF and rhIGF-I treatment on serum IGFBPs and mRNA for IGFBPs and IGF-IR. METHODS: Rats with ARF and sham-operated control rats were randomized to receive rhIGF-I or vehicle injections thrice daily for 72 to 74 hours starting five hours after surgery. Serum IGFPBs 1 to 6 were measured serially, and mRNA for IGFBPs 1 to 6 and for IGF-IR were measured in several tissues obtained 72 to 74 hours after surgery. RESULTS: At 72 to 74 hours, serum IGFBP-1 and IGFBP-2 levels were higher in rhIGF-I treated rats. Serum IGFBP-3 was affected by both ARF and rhIGF-I. IGFBP-4 rose transiently only in ARF groups. At 72 to 74 hours, mRNA for several IGFBPs was reduced in renal cortex of ARF rats. Low mRNA for IGFBP-4 and -6 was observed in renal medulla of the ARF rats, particularly in comparison to the sham-operated rats receiving vehicle. Renal medullary IGFBP-2 mRNA was decreased in ARF and sham rats given rhIGF-I as compared to sham animals given vehicle. Hepatic IGFBP-2 mRNA was higher in both rhIGF-I treated groups versus those given vehicle. Otherwise, there were no differences in IGFBP mRNAs among the four groups in lung, heart, and skeletal muscle. IGF-IR mRNA was decreased in renal cortex and medulla of both ARF groups and was not detected in liver in any group. CONCLUSIONS: Thus, ARF and rhIGF-I treatment each affected certain serum IGFBPs and jointly affected some IGFBPs. ARF suppressed gene transcription for renal cortical and medullary IGF-IR and some IGFBPs. rhIGF-I independently affected some renal cortical or medullary IGFBP mRNAs. rhIGF-I increased hepatic IGFBP-2 mRNA and serum IGFBP-2. These effects of ARF or rhIGF-I may influence rhIGF-I actions in rats with ischemic ARF.

Acute Kidney Injury↗
PubMed1998

Control of clonorchiasis by repeated praziquantel treatment and low diagnostic efficacy of sonography.

In Korea, Clonorchis sinensis infection is still highly prevalent because case detection in the field is difficult and the detected cases used to be incompletely cured due to treatment failure. The present study tried to control clonorchiasis in an endemic village by repeated treatments with praziquantel every 6 months and to evaluate sonography as a diagnostic measure. By stool examinations, the egg positive rate in the endemic village was 22.7%, but it decreased to 19.6% at 6 months, 15.1% at 12 months. 12.2% at 18 months, 6.3% at 24 months, 11.4% at 30 months, and 6.3% at 42 months after the beginning of repeated praziquantel administration. The sonography showed 61 (49.6%) positive cases of 123 screened residents: among egg-positives the sonography positive rate was 52.2% and among egg-negatives it was still 49%. The rate among cured cases was 64.3% after 6 months, 50.0% after 12 months, 50.0% after 18 months, and 66.7% after 24 months. In a non-endemic village, 64 residents were found egg-negative by fecal examination, but 20 (31.3%) of them were positive by sonography. The present findings indicate that control of clonorchiasis in an endemic village by repeated praziquantel treatment for 42 months is still insufficient and sonography is of little value for diagnosis of clonorchiasis.

Animals↗